The present invention relates to a developing device and an image forming apparatus having the developing device.
In a conventional image forming apparatus of an electric photography type such as a printer, a copier, and a facsimile, or a multifunctional product (NFP) having more than two such functions, a charging roller uniformly charges a surface of a photosensitive drum, and an exposure unit exposes the surface to form a static latent image thereon. A developing unit develops the static latent image to form a toner image. A transfer roller transfers the toner image to a sheet, and a fixing unit fixes the toner image to form an image, thereby printing the image on the sheet.
FIG. 2 is a view showing an essential part of a conventional printer. As shown in FIG. 2, the conventional printer includes an image forming unit 11; a photosensitive drum 12; a charging roller 13; and a developing device 14. The developing device 14 includes a developing roller 16; a developing blade 17; and a toner supply roller 18. The conventional printer also includes a cleaning unit 15; a developer storage space 20; a toner cartridge 21; and a toner supply port 22.
A stirring member 25 formed of a shaft with a crank shape is disposed in the developer storage space 20 above a contact portion between the developing roller 16 and the toner supply roller 18. The stirring member 25 stirs toner in the developer storage space 20 supplied from the toner cartridge 21 through the toner supply port 22. The stirring member 25 also prevents agglomerated toner or a foreign matter in toner from staying near the contact portion (refer to Japanese Patent Publication No. 2002-108089).
As described above, in the conventional printer, the stirring member 25 prevents agglomerated toner or a foreign matter in toner from staying near the contact portion. However, the stirring member 25 is not capable of transporting toner in an axial direction. Accordingly, over the time while toner in the developer storage space 20 is consumed and new toner is supplied, toner tends to accumulate at both sides of the developer storage space 20. In this state, when the printer performs printing, it is difficult to obtain good dot reproducibility and graininess at both sides of an image as opposed to a center thereof, thereby deteriorating image quality.
In view of the problems described above, an object of the present invention is to provide a developing device and an image forming apparatus for forming an image with improved image quality.
Further objects and advantages of the invention will be apparent from the following description of the invention.